How to make edges smoooth/rounded?
Your topology is not good so the bevel won't work properly, what you can do is:

First apply the scale, otherwise the bevel will be deformed on an axis:



Go in Edit mode, you have a lot of triangles, a quick way to fix it is to select all and X &gt; Limited Dissolve (the default settings will work fine):


Delete the top faces with X &gt; Faces:


You need to delete some rebel vertices along the edge with X &gt; Dissolve Vertices:



Enable the LoopTools addon, select the top edges and right click &gt; LoopTools &gt; Bridge to create new faces:



Select the top edges and CtrlB to bevel. You can tweak all the settings in the Operator box (bottom left of your 3D view):